There are various toys and games on the market that generate a color change or glow. Some toys change color upon contact with water (e.g., U.S. Pat. No. 6,416,853 describes a diaper of a baby doll that turns yellow when exposed to water.) Another type of toy changes color when exposed to heat or cold (e.g., U.S. Pat. No. 5,716,253 involves a toy frying pan with bacon and eggs that changes color when placed over ice.) Other types of toys and games change color when physically deformed, such as a ball that can be squeezed to reveal the color of its inner core. (e.g., see U.S. Pat. No. 6,905,431.) Still another type of toy changes color using magnetic particles, as discussed in U.S. Pat. No. 7,607,919.
Although the above toys and games work well for various applications, there are ongoing efforts to make toys and games more educational and engaging for children.